What switches are you using?
Do you have a constant AC source?
You want to do AC clipping or you want to control the outputs of the flyback transformer individualy like with triacs?
You have an schematic?
For what I can put together here You want to control and regulate the output voltage of an AC source to a lower AC voltage with some type of switcher IC is this IC operating on DC?.
Or you just want to use a Flyback transformer to build a DC regulated power supply?